Heat Energy

- Heat occurs when MOVING PARTICLES GENERATE FRICTION through collisions.

 

KINETIC THEORYstates that all matter is made up of particles that are constantly in motion.

Pick a particle in the simulation and follow it for a whole cycle of random motion. Heat occurs whenever two particles come in contact.

The faster the particle, the higher its temperature. The slower the particle, the lower its temperature.

A particle that isn't moving has NO temperature. This is called absolute zero. You may find a particle that seems to be still for a moment but it won't be long before it is knocked around by a faster one!

 

ADDING heat to particles will cause two things...

1. SPEED UP

2. SPREAD OUT (EXPAND)

 

REMOVING heat from particles will cause two OPPOSITE things to happen...

1. SLOW DOWN

2. GET CLOSER TOGETHER (CONTRACT)

 

examples of examples of thermal expansion
 
 

 

Thermal Energy (heat) is not the same as temperature.
Heat energy
Temperature

The total amount of friction between all the particles in a substance.

Can be calculated with the formula:

H=mct

Heat = (mass)(specific heat)(change in temperature)

The average speed of the particles in a substance

Measured with a thermometer.

metric: degrees Celsius or Kelvin

English: Fahrenheit

Compare a burning match with an iceberg..

Which has a higher temperature?

Which has more thermal energy?

The match has faster moving particles than the iceberg. A thermometer would read higher in the flame than buried in ice.

A burning match has a higher temperature than an iceberg.

The iceberg has a GREAT deal more molecules moving around than the match stick. Try melting an iceberg with a match.

The iceberg has more heat (thermal energy) than a burning match.

Not convinced yet? Try this question.

Would you rather get a $1000 bill or a penny from everyone in St. Louis?

A penny isn't much (like the motion of ice particles) but when multiplie a few million times it amounts to a prize much greater than the large bill.

 

Heat flows from HOT to COLD until the temperatures are the same. When objects have the same temperature we say they are in "equilibrium".

 

HomeLab: Go to your refrigerator and feel around the back. What do you feel? You should be feeling warmer. This is the heat that used to be in your food. The refrigerator pumps the heat from the inside to the back. As long as it is plugged in, the inside will be losing its heat. Most people would say it "feels" cold in there.

Challenge Question: You take a temperature reading in the kitchen. If you opened the refrigerator door and left it open, what would happen to the temperature in the kitchen?

 

 

It is important to understand that there is no such thing as cold! "Hot" and "cold" are words that DESCRIBE the amount of heat.

If I give you money you would be "rich". If I take your money you could be described as "poor".

I cannot give you poor.

If I give you heat energy you would be "hot". If I take away your heat energy you could be described as "cold".

I cannot give you cold. I can only give and take HEAT

 

Most people don't quite GET this point.

For example, it's a cold winter day and you leave the door open when coming in from playing in the snow. Mom screams from the other room "CLOSE THE DOOR, YOU'RE LETTING IN THE COLD!!"

 

You could say "Uh-hem, Mother, I'm not letting in the cold. I learned in science that basic laws of physics state that heat will flow TO a space that has less heat. Therefore, when I leave the door open I'm really letting OUT the heat that you have spent your hard-earned money on to keep our house comfortable."

(I wouldn't recommend it though. Just close the door and be happy you're alive. Needless to say, you should probably not give Mom a lesson on keeping heat OUT when you leave the door open in the summer when the AC is on OR when you hang out with the refrigerator open when you choose your snack. )

 

 

Heat is transferred in 3 different ways

1. conduction

direct contact between objects of different temperatures.

If you were to touch a hot skillet the heat energy would travel FROM the skillet TO your hand.

If you hold a snowball in your hand, it feels cold because the heat is leaving FROM your body and going TO the snow.

The snow melts because of YOUR heat!

You come into science class and the chair is cold. Sitting on a cold chair will start a battle between the particles in your body and the particles of the chair. Heat flows from hot to cold until the temperatures (speed of the particles) are the same.

Eventually the chair will feel warm. This means you are not needing to pass heat to the chair anymore. You and the chair are the same temperature.

If a material lets conduction happen quickly we say it is a "good CONDUCTOR"

(it would then be a poor insulator)

examples include:

copper, iron, gold, metals in general

If a material makes conduction happen slowly we say it is a "good INSULATOR"

(it would then be a poor conductor)

examples include:

cotton, wool (hair),carpet, plastics, air, water, styrofoam, a vacuum (empty space)

 

Water is a fantastic absorber of heat. Check out this demonstration below. As long as there is water in the cup the paper WILL NOT BURN!

 

 

Heat is transferred in 3 different ways

2. convection

the flow of heat through liquids or gases (fluids)

   

Watch what happens when the red and blue dye reveal the current flow in this aquarium. This flow is a great example of CONVECTION!

 

 

DAYTIME

SEA BREEZE

Imagine Florida being heated by the sun. The air above Florida speeds up, spreads out, becomes less dense and rises. The cool air from the Gulf, Atlantic and Caribbean moves in to take its place. This is called a sea breeze.

At night the reverse takes place because the land is cooler than the water.

NIGHTTIME

LAND BREEZE

When warm moist air is lifted into the cooler atmosphere by convection, clouds are formed. Thunderstorms are the result of incredible convection. Watch this "supercell" cumulonimbus cloud form.

 

 

 

Heat is transferred in 3 different ways

3. radiation

-an electromagnetic wave at the speed of light (infrared)

Click on "Radiant" energy to learn more about heat that is really a form of LIGHT.

A campfire gives off all three heat transfers.

The logs and stones get HOT. Touching the logs would transfer heat to you.

This is conduction.

The heated air rises above the campfire. Cool air makes the camper's back cold.

This is convection.

The marshmallows are being cooked and the front of the camper is becoming warm.

This is infrared radiation.

 

Some things heat up quicker than others.

because they are made of different materials

It's 2:00 in the afternoon and not a cloud in the sky. You've been under the shade of your umbrella for a while and you want to take a swim.

 

You step out barefoot from your umbrella and begin walking across the beach to the ocean.

OUCH! is an understatement.

The sand is painfully hot! You run across the sand as fast as you can.

 

Finally you splash into the cool blue ocean. Your feet don't seem to be burning anymore. Why?

The sun has been beating on the sand AND the ocean equally all day long.

Why would the sand be HOT and the ocean NOT?

 

Answer #1:

The ocean is bigger than the beach. It takes more heat energy to raise the temperature of big things.

Answer #2:

The ocean is a fluid. The heat is constantly being moved around.

Answer #3:

Water and sand have different SPECIFIC HEATS.

Specific heat is the amount of energy it takes 1 gram of a substance to raise in temperature by 1 degree Celsius.

Specific heat tells us how quickly a substance will heat up or cool off.

Download a chart listing the specific heat of many substances HERE. Don't even think about memorizing it though...that's why we make charts in the first place. One day you may use these numbers so much you remember them but not yet.

Some things heat up quicker than others.

because they are different colors.

 

When light hits an object , two things can happen to the energy...

1. light is absorbed by the object and transformed into HEAT

2. light is reflected away still as light.

Black ABSORBS all of the colors of the rainbow.
White REFLECTS all of the colors of the rainbow.

Colored objects reflect SOME and absorb SOME. We "see" the only colors that are reflected off the object to our eyes.

More absorbed light will equal more heat!

 

If enough heat is added or removed the particles will

CHANGE STATE.

 

 

ENERGY

BASICS

Chemical

Heat

Electro - magnetic

Mechanical

Nuclear

Radiant

Sound

 

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